Ukraine fears spread of war after blast in eastern city

Kiev said it arrested four people who had been armed and trained in Russia after the blast, which killed a policeman and a demonstrator at the rally in Kharkiv, the biggest city in the east, ۲۰۰ km(۱۲۵ miles) from the war zone.

A week after a ceasefire agreement that Moscow - backed rebels ignored to capture a strategic town, Kiev and its Western allies are trying to determine whether the separatists will now halt, or advance deeper into territory the Kremlin calls " New Russia ".

Germany and France mediated the peace deal that came into effect a week ago, and say they still hope it can be resurrected, even though the rebels ignored it to inflict one of the worst defeats of the war, seizing the town of Debaltseve after encircling thousands of Ukrainian troops.

In signs that there may be at least a pause now that the rebels achieved that objective, government and separatist forces exchanged prisoners overnight. The rebels said on Sunday they would begin withdrawing artillery from the front.

But Kiev said Moscow was moving more troops and armor into eastern Ukraine near a port it fears is the next target. Russia denies it has troops in eastern Ukraine.

" TERRORIST SCUM "

Ukrainians held marches and memorial services on Sunday for ۱۰۰ people killed a year ago during an uprising that toppled a pro - Russian president and led to the war in which more than ۵,۵۰۰ people have since been killed.

At the rally in Kharkiv, amateur footage posted on the Internet showed a few hundred marchers with Ukrainian flags, who shouted " glory to the heroes! " just before being hit by an explosion. Demonstrators and bystanders, including a woman pushing a baby in a pram, fled in panic. A wounded man in military uniform lay in the snow shouting for help.

" Today is memorial Sunday, but on this day terrorist scum revealed its predatory nature, " President Petro Poroshenko said on Facebook. " This is a brazen attempt to expand the territory of terrorism. "

A Reuters journalist at the scene later filmed the bodies of two men lying by the road, draped in blue and yellow Ukrainian flags and surrounded by shrapnel.

Demonstrator Igor Rossokha told Reuters Television his friend Igor was one of those killed: " We tried to give him first aid, but the paramedics arrived and said he’d died instantly because he was struck in the heart. "

Kiev has long worried that Russia aims to foment instability far beyond regions now held by separatists. Kharkiv, with ۱.۴ million people, has occasionally seen violent protests by separatists in the past year but is firmly under Kiev’s control.

Markian Lubkivskyi, an aide to the head of Ukraine’s SBU security service, said four arrested suspects planned a series of attacks in the city with a Russian " Shmel " rocket launcher.

" They are Ukrainian citizens, who underwent instruction and received weapons in the Russian Federation, in Belgorod, " he told Ukraine’s ۱۱۲ Television. Belgorod is a city across the nearby Russian border from Kharkiv.

Moscow did not immediately respond to the accusations. It has long denied aiding its militant sympathizers in Ukraine.